Javascript: Overriding XMLHttpRequest.open()

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You are not modifying the open method inherited by XMLHttpRequest objects but just adding a method to the XMLHttpRequest constructor which is actually never used.

I tried this code in facebook and I was able to catch the requests:

(function() {
    var proxied = window.XMLHttpRequest.prototype.open;
    window.XMLHttpRequest.prototype.open = function() {
        console.log( arguments );
        return proxied.apply(this, [].slice.call(arguments));
    };
})();

/*
    ["POST", "/ajax/chat/buddy_list.php?__a=1", true]
    ["POST", "/ajax/apps/usage_update.php?__a=1", true]
    ["POST", "/ajax/chat/buddy_list.php?__a=1", true]
    ["POST", "/ajax/canvas_ticker.php?__a=1", true]
    ["POST", "/ajax/canvas_ticker.php?__a=1", true]
    ["POST", "/ajax/chat/buddy_list.php?__a=1", true]
*/

So yeah the open method needs to be added to XMLHttpRequest prototype (window.XMLHttpRequest.prototype) not XMLHttpRequest constructor (window.XMLHttpRequest)

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